This invention relates to thermoset resin impregnated fibrous web battery separators, filters and other semi-rigid products, and to the curing of thermoset resin on thermoplastic members, particularly those having melting, Vicat softening or shrinking by more than 5% points below the curing temperature of the thermoset resin.
A porous battery separator sheet made from 50% glass fiber and 50% cellulosic pulp impregnated with 121/2 to 30% thermosetting resin is revealed in U.S. Pat. No. 2,687,445. A lead acid battery separator containing fibrous polyolefin synthetic pulp, particulate siliceous filler, long paper making staple fiber and optionally up to 10% cellulosic fiber but not impregnated with a thermosetting resin is shown in co-pending application, U.S. Ser. No. 935,280, filed Aug. 21, 1978, now U.S. Pat. No. 4,216,281, and assigned to the same assignee as the present application. As far as is known, a polymeric synthetic pulp has never been used in a web impregnated with a thermoset resin. The addition of such a synthetic pulp to such a web has been found to provide a product having unique properties. Surprisingly it has been found that thermoplastic synthetic pulps can be used even when the thermo-setting temperature to be used in curing the resin will exceed the Vicat softening point and even the melting point of the synthetic pulp. Thus, for example, the cellulosic fibers in such a web can be protected from the deleterious corrosion of a battery environment.
It is one object of the present invention to provide a new porous web that has chemical resistance and substantial rigidity combined with significant flexibility without brittleness.
It is a further object of the present invention to provide a new and improved battery separator.
It is another object of the present invention to provide an improved porous sheet containing synthetic fibers that has improved stiffness with fracture resistance, improved chemical resistance, superior delamination resistance, superior inter-fiber bonding, improved thermal resistance and resistance deterioration on aging.
A further object of the invention is to provide a process for manufacturing a web containing cellulosic fiber and at least 5% by fiber weight polyolefin synthetic pulp and impregnated with 10 to 50% by weight of a thermoset resin based on the weight of the fiber.
A still further object of the invention is to provide a process that will maintain the flexibility of a thermoplastic synthetic pulp while setting a thermosettable resin thereon at a temperature above the softening or the Vicat melting point of the thermoplastic polymer of which the synthetic fibers are composed.